Environmental Contamination of Heavy Metals and Effects of Sediment Bacteria on Cadmium Speciation in the Vicinity of the Hwacheon Mine

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In order to investigate the extent and degree of heavy metal contamination in soils and sediments influenced by past mining activities, and to estimate the effects of indigenous bacteria on Cd speciation and bioremoval efficiency in sediments according to the various environmental conditions, tailings, soils, waters and sediments were collected from the Hwacheon Au-Ag-Pb-Zn mine in Korea. Elevated levels of metals, i.e., 29 As mg/kg, 30 Cd mg/kg, 261 Cu mg/kg, 601 Pb mg/kg and 3128 Zn mg/kg were found in sediments. High concentrations of As and other heavy
metals in soils, waters and sediments were found near the tailings piles. From the results of sequential extraction analyses with tailings and soils, a high proportion of Cd is present as non-residual fractions. This indicates that Cd is more mobile and bioavailable than Cu, Pb and Zn. For seasonal variation, the concentrations of As and other heavy metals were much more elevated in soils collected before rainy
season than after rainy season. To estimate the bioremoval efficiency for Cd, bacteria which can adsorb Cd were isolated from sediments in this area. Microorganisms in sediments can alter the mobility of heavy metals and bacteria can leach heavy metals from sediments, adsorb them on their cell wall and accumulate them within an intracellular matrix. From the metal sorption tests with indigenous bacteria, the bioremoval efficiency of Cd in Cd single solution (10 ppm) was more than 90%. As well, the isolated bacterial strains exhibited a preferential metal sorption , i.e., Cd > Pb > Zn for single metal solutions and Pb > Cd > Zn for the mixed metal solutions. Therefore, the use of some microorganisms to remove heavy metals from contaminated sediments may represent an innovative purification process.

Abstract: Various depths paddy soils, which collected from nearby one of the abandoned Pb-Zn mines in Lanping County of China, were analyzed, determining the total metal concentration by acid digestion and the chemical speciation of Zn, Pb, Cu and Ni by a somewhat modified Tessier’s sequential extraction method. High concentrations of Zn and Pb were found in surface soils indicating that the paddy soils seriously suffered from Zn and Pb contamination. The extraction percentage of Zn, Pb, Cu and Ni with modified Tessier’s sequential extraction procedures were at the ranges of 93.15-96.41%, 93.26-96.25%, 91.51-94.75% and 91.28-94.25%, respectively. Extraction efficiencies demonstrated that this sequential extraction approach is suitable to evaluate these metals potential risk among this contaminated site. Extraction results showed that the residual fraction was the predominant fraction for Zn, Pb, Cu and Ni among all tested soils. However, the exchangeable fraction was the lowest among all fractions. Meanwhile, the metals mobility and bioavailability in tested soils were compared and predicted using mobility coefficients and bioavailability coefficients. The mobility coefficients of metals decreased in the order of Cu> Ni> Zn> Pb, and the bioavailability coefficients of metals decreased in the order of Pb>Cu>Zn/Ni.

Abstract: The total contents and chemical phase partitioning of Cd, Ni, Cu, Zn and Pb from long-time sewage- irrigated soil were analyzed in this paper. The results showed that the contents of Ni, Cu, Zn, and Pb did not exceed the the second-level limit of Standard of Soil Environment (GB15618-1995), but the average content of Cd was 1.81 mg•kg-1, which was about three times more than the national standard. The chemical partitioning of metals analysis showed that Cd was present dominantly in the acetic acid extractable fraction with the average percentage of 37.44%, while the other four elements mostly in residual fraction, which indicated that Cd had the highest bioavailability, mobility and phyto-toxicity. Compared to the well-irrigated soils, the percentages of acetic acid extractable fractions of Cd, Ni, Zn and Cu were obviously higher in the contaminated soils, which increased the potential danger of heavy metals pollution.

Abstract: A pot experiment was conducted to investigate the effects of attapulgite clay, activated carbon, and liquid organic fertilizers used as soil amendments on cadmium (Cd) and lead (Pb) immobilization as well as on tobacco growth in contaminated soils. All three amendments reduced the amounts of DTPA-extractable Cd and Pb in soils as well as the concentrations of Cd and Pb in tobacco roots and leaves, compared to the control. Cadmium had a higher transportation index into tobacco leaves than Pb. DTPA-extractable Cd and Pb in soils was positively correlated with the metal concentrations in tobacco leaves, suggesting that DTPA-extractable Cd and Pb measurement could be a feasible method for assessing Cd and Pb bioavailability. Experimental results showed that upward trends of Soil and Plant Analyzer Development (SPAD) value in leaves were observed when tobaccos plants were grown in contaminated soils with increases of all the amendments. There were increases in root and shoot lengths as well as leaf area and dry weight for tobacco grown in amendment treated soils compared to the control.

Abstract: Concentrations of lead in roadside soils from different function areas of Suzhou City were determined and analysed by X-Ray fluorescence spectrometer, and the method of geoaccumulation index. The results indicate that the concentrations of lead in roadside soils range from 23 to 90 mg/kg, with an average value of 37.11 mg/kg, exceeded the environment background value; the lead concentration from high to low is commercial areas, areas around station, industrial areas, urban green space and residential areas; most of roadside soils have not been polluted or only slightly polluted, except sampling site 19, 23 and 49 (moderate pollution).

Abstract: In a laboratory incubation study, two soils were treated with distilled water, and flooded for a period of 0 (contr-ol), 1, 2, 3, 4, 8 weeks. P adsorption desorption characteristics of two soils were measured at the end of the incubation period. P a-dsorption increased with increasing levels of added P in two soi-ls. P adsorption of Paddy soil was comparatively lower than that of upland red soil. P adsorption data was found to fit Langmuir isotherms for two soils. Soil P adsorption maxima obtained from Langmuir isotherm varied from 1190 to 672 mg/kg for upland r-ed soil, and varied from 708 to 530 mg/kg for paddy soil. Floodi-ng decreased P adsorption capacity of upland red soil,increased soluble P (in 0.01M CaCl2) and equilibrium P concentration. For paddy soil, there was a large increase in the P sorption capacity after one week flooding, and then P sorption capacity decreased. The more adsorption maxima is, and the more desorption maxi-ma (Dm) is. Desorption rate constant (Kd) and bonding energy (b) varied inconsistently in two soils.